Polystyrene composition plasticized with pyrolyzed polyethylene and method of preparation



United States Patent Ser. No. 686,843

11 Claims. (Cl. 26033.6)

This invention relates to a novel hydrocarbon material. In one aspect,this invention relates to a process of pyrolysis. In another aspect, itrelates to a plasticized polystyrene composition and a method ofpreparing the same.

This application is a division of our copending appli cation Serial No.479,681, filed January 3, 1955.

t is known in the prior art to pyrolyze certain polyethylenes to obtainproducts of lower molecular weight. The present invention provides amethod for the production of novel pyrolysis products by utilizing, as afeed to the pyrolysis process, an olefin polymer prepared assubsequently described.

Polystyrenes and the production thereof are well known in the art. Theproperties of a particular polystyrene resin are to some extentdependent upon the method of preparation thereof. Certain polystyreneresins are quite brittle at low temperatures Whereas some are relativelytough and not brittle. As a general rule, however, the polystyrenes arediflicult to mold, particularly when it is desired to prepare largemolded articles. Numerous dilferent materials have been proposed asplasticizers for polystyrene resins, but, in many cases, satisfactoryresults have not been obtained. In some cases, it is necessary to addrelatively large amounts of plasticizers in order to obtain the desiredplasticity. In other cases, the addition of plasticizers yields tackycompositions having low tensile strength. In many cases, theplasticizers are not compatible with the polystyrene and it is,therefore, impossible to produce clear, transparent, molded productstherefrom.

This invention provides a novel material utilizable as a polystyreneplasticizer, a novel plasticized polystyrene resin composition and amethod of production thereof.

According to this invention, novel pyrolysis products are obtained bypyrolyzing, or thermally decomposing, or cracking, a high molecularweight polymer, especially a polymer of at least one l-olefin having amaximum chain length of 8 carbon atoms and no branching nearer thedouble bond than the 4-position, said polymer having been produced bypolymerization in the presence of a composite catalyst which compriseschromium oxide as an essential ingredient.

The pyrolysis according to this invention is carried out at atemperature in the range 600 to 1200 F.

The polymeric material which is subjected to pyrolysis according to thisinvention is prepared according to methods more fully set forth in thecopending application of Hogan and Banks, Serial No. 476,306, filedDecember 20, 1954, and now abandoned, a continuation-in-part of which isnow U.S. 2,825,721. In brief, this method comprises contacing an olefin,such as ethylene, propylene, l-butene, l-pentene and/0r l-hexene, at atemperature in the range 150 to 450 F. with a catalyst comprising, asits essential ingredients, from 0.1 to 10 or more weight percentchromium in the form of chromium oxide, including a substantialproportion of hexavalent chromium, associated with at least oneadditional oxide, especially at least one oxide selected from the groupconsisting of silica, alumina, zirconia, and thoria. This catalyst, in

one of its preferred forms, is a highly oxidized catalyst which has beenactivated by high-temperature treatment with an oxidizing gas. Thepolymerization is usually carried out with the monomeric olefin insolution in a hydrocarbon solvent, especially a paraffin or a naphthenewhich is liquid under the polymerization conditions. The polymersdecomposed by pyrolysis according to the present invention have amolecular weight of at least 5,000, and the molecular weight can be ashigh as 200,000

or more.

The pyrolysis products according to this invention have numerous uses,such as starting materials for alkylation processes wherein aromaticsare alkylated with the said products to produce lubricating oiladditives and/ or intermediates for the production of surface-activematerials. The pyrolysis products are particularly valuable asplasticizers.

Further according to this invention, a polystyrene resin compositionhaving improved molding properties is obtained by blending with apolystyrene resin produced by any of the methods known in the prior art,a minor proportion, suflicient to plasticize said polystyrene, of apyrolysis product prepared as previously described herein.

Hydrocarbon compositions, according to this invention, having molecularweights in the range 200 to 800 which are linear in character, containterminal vinyl groups, terminl methyl groups, and trans-internalunsaturation, are obtained by heating specially prepared solidpolyethylenes at a temperature in the range 700 to 900 F. anddistilling. It is generally preferred that the thermal treatment beeiiected in the absence of air. The solid polyethylene employed as thestarting material is prepared by the polymerization of ethylene atrelatively low pressures over a composite chromium oxide polymerizationcatalyst, as more fully described in the cited application of Hogan andBanks.

In the preparation of the pyrolysis products of this invention, theproducts can be distilled simultaneously with the thermal treatment.When operating in this manner, the overhead temperature for thedistillation is in the range between 400 and 600 F., and pressures notexceeding about mm. Hg are employed. Said pressures preferably do notexceed 25 mm. Hg, and, still more preferably, they do not exceed 15 mm.Hg. If desired, the polyethylene can be subjected to the thermaltreatment (pyrolysis) at atmospheric pressure and pyrolysis temperature,as indicated above, generally using an inert gas blanket, such asnitrogen, and the pressure can then be reduced prior to distillation.

The olefinic compositions prepared in the manner described, according tothis invention, are slightly yellow, waxy solids which have averagemolecular weights in the range between 200 and 800. They differ fromproducts prepared in a similar manner fromother polyethylenes. Theproducts of this invention have linear carbon chains, i.e., they havevery little, if any, branching. On the other hand, products preparedfrom other polyethylenes appear to contain considerable branching. Thedouble bonds present in the products of this invention are present asterminal vinyl groups and as trans-internal double bonds with very few,if any, branched vinyl groups being present. On the other hand, productsobtained by the thermal treatment of other polyethylenes contain smalleramounts of terminal vinyl groups and transinternal double bonds but, inaddition, contain so-called branched vinyl groups in considerablepercentage. Infra-red spectroscopic study indicates that pyrolysisproducts obtained from certain commercial polyethylenes contain a largernumber of methyl substituents than are present in the compositions ofthis invention. The methyl groups which can be detected by infraredspectroscopy include those connected to internal carbon atoms of long 3chains, as well as terminal methyl groups on the longer carbon chains.

Terminal vinyl groups and trans-internal unsaturation may be representedin the following manner:

H: H o 0 Ha H H:

Trans-internal Ha I o /C-H o o H, H Terminal vinyl Branched vinyl groupsmay be represented in the following manner:

The olefinic compositions of this invention can be blended with variousresinous materials to modify the properties of the latter. One importantuse is in blends with polystyrene to give compositions having improvedmolding characteristics, as compared with polystyrene alone.

It has been found that, by blending a minor amount of the pyrolysisproduct of this invention with polystyrene, clear molding compositionsare readily obtained which have a much higher melt index thanpolystyrene alone and, therefore, have improved flowing propertiesduring molding operations, as compared with polystyrene alone. (Meltindex, as determined by ASTM Method D1238- 52T, is the rate of extrusionof a thermoplastic material through an orifice of a specified length anddiameter, under prescribed conditions of temperature and pressure.)

The other physical properties of the new polystyrene moldingcompositions, according to this invention, including impact resistanceand tensile strength, are also very satisfactory. The amount ofpyrolysis product employed is, generally, in the range 0.2 to 20,preferably 0.5 to 8, weight percent, based on the polystyrene.

-method, the mixing is done at an elevated temperature.

The polystyrene should be at -a temperature high enough that it can bemilled. The temperature will depend upon the polystyrene employed and isordinarily in the range 150 to 325 F.

The molding compositions of this invention are applicable for the manyuses already known for polystyrene.

.On account of their excellent molding characteristics,

they are particularly applicable for making large molded objects, sincethe material can be caused to flow smoothly into corners and over largeareas. These compositions can be shaped by compression or injectionmolding to yield smooth, lustrous objects.

Example I Ethylene was polymerized over a fixed bed of chromiumoxide-slica-alumina catalyst, containing 2.48 weight percent chromium aschromium oxide, at 320 F., 450 p.s.i.g., and a space velocity (volumesliquid/volume catalyst/hour) of 5, the feed containing 2.5 weightpercent ethylene in isooctane (2,2,4-t1imethylpentane). The

4 ethylene feed rate was 2.24 pounds per hour. The polyethylene obtainedhad a density of 0.956 at 20 C., a melting point of 243 F., and amolecular weight of 11,080, as determined by intrinsic viscositymeasurement utilizing a solution of the polymer in tetralin.

Six hundred eighty grams of polyethylene prepared as described above wascharged to a stainless steel pot, 1 percent by weight2,6-di-tert-butyl-4-methylphenol (Ionol) was added in order to inhibitany possible oxidation, the pot was flushed with nitrogen, evacuated toa pressure of 1 mm. Hg and heated gradually to 730 F. over a period of 5hours. The pot temperature was maintained at 730 to 750 F. for about 3to 4 hours, during which the pyrolysis product was continuouslydistilled off at an overhead temperature of 520 to 570 F. The pressureduring the distillation was 7 to 8 mm. Hg. The product taken overheadweighed 327 grams and had a molecular weight (determined by benzeneboiling point elevation) of 327. It was a slightly yellow, waxy solid.This material is hereinafter designated as product A.

Four hundred forty-four grams of a commercial polyethylene not producedby use of a chromium oxide catalyst and having a molecular weight ofapproximately 12,000 was charged to a stainless steel pot, 1 percent byweight 2,6-di-tert-butyl-4-methylphenol was added, the pot was flushedwith nitrogen, evacuated to a pressure of 1 mm. Hg, and heatedgradually, over a period of 1 /2 hours, to 725 F. At this point, thematerial began to distill. During the distillation, which was continuedfor 4 to 5 hours, the pot temperature remained at 725 F. and theoverhead temperature was 478 to 480 F. The pressure during distillationwas 7 to 8 mm. Hg. The product was a wax-like material having amolecular Weight of 346. This material is hereinafter designated asproduct B. The yield was lower than that of product A, a larger amountof gaseous pyrolysis product being formed.

Infrared analyses were run on the two products A and B. The followingresults were obtained:

Infrared data were compared in the following manner against themolecular Weight values obtained by boiling point elevation for each ofthe materials:

Product Product A B Molecular weight by benzene boiling point elevation327 346 Number of carbon atoms per molecule:

Number of double bonds per carbon atoms:

(0.5) (100)/23.3 a. 2.14 (0,4) (low/24.7 1.62 Terminal vnyl groups per100 carbon atoms 7 1. 8 .r (1.62) (0.66) 1.07 Total end groups (methyland vinyl) per 100 carbon atoms:

7.0+l..78 8. 78 8.4+1.07 9. 47 Molec es per 100 carbon atoms (assumingeach molecule to have only two end groups):

8.78/2 4. 39 9.47/2 4. 73' Number of carbon atoms per molecule: loo/4.3922.8 loo/4.7a 21.1 Molecular weight calculated from infrared analysis:

1 The weight r a om group is 14.

The last-mentioned molecular weight of product A, calculated fromboiling point elevation together with the results of the infraredanalysis, is in reasonably close agreement with that obtainedexperimentally by the boiling point elevation method. For product B, thedifferonce is quite large. It is believed that branching in product Baccounts for the difierence in molecular weight as calculated frominfrared analysis from that determined by boiling point elevation. Theseresults at least indicate that there is a fundamental difference betweenproduct A and product B, since the foregoing assumption that product Ahas only two end groups (and is, therefore, linear) is much more nearlycorrect than the same assumption for product B.

Example 11 Ethylene was polymerized over a fixed bed of chromiumoxide-silica-alumina catalyst, containing 2.46 weight percent chromium'as chromium oxide, at 310 to 330 F., 400 p.s.i.g., and a space velocity(volumes liquid/volume catalyst/ hour) of 5, the feed containing 2weight percent ethylene in isooctane. The ethylene feed rate was 1.80pounds per hour. The polyethylene o tained had a density of 0.956 at 20C, a melting point of 242:1 F., and a molecular weight of 11,650, asdetermined by intrinsic viscosity measurement utilizing a solution ofthe polymer in tetralin.

Five hundred grams of the polyethylene, prepared as described above, wascharged to a 2-liter pot which was then flushed with nitrogen, evacuatedto a pressure of 1 mm. Hg and heated gradually to 800 F. The pottemperature was maintained at 800 F. and the overhead temperature at 500to 550 F. The pressure during the distillation was 4 mm. Hg. The producttaken overhead weighed 320 grams and had a molecular weight (determinedby benzene boiling point elevation) of 335. It was a slightly yellow,waxy solid. This material is hereinafter designated as product C.

Ch'ystallinity was determined by X-ray diiiraction on the pyrolysisproduct (product C) and on a sample of the pyrolysis product describedin Example I (product B). Product C showed much greater crystallinitythan product B. Data obtained were as follows:

Percent crystallinity Product C l5 ProductB 7 Example Ill Portions ofproduct C (Example 11) were blended on a hot mill (300 F.) with thepreviously mentioned general-purpose polystyrene. Three runs were madeusing 5, l and 15 weight percent of the polyethylene pyrolysis product,based on the polystyrene. The pyrolysis product formed homogeneousblends with the polystyrene but in the last two runs, some cloudinessappeared in the mixture, which indicated incompatibility of thepyrolysis product with the polystyrene. In the run containing weightpercent of pyrolysis product, the product remained clear. Physicalpropertieswere determined on the blends Polyethylene in Impact, HeatDis- Tensile, Elonga- Melt Blend, Wt. ft./lbs./ tortion, p.s.i. tion,Index 2 Percent 111. 0. Percent 1 ASTM D 25647 T, cantilever beam test(Izod type).

2 AS'IM D 1238-52 T, rate of extrusion of a thermoplastic materialthrough an orifice of a specified length and diameter under prescribedconditions of temperature and pressure.

The data show that the polystyrene plasticized according to thisinvention had improved properties, especially increased melt index.

Example IV Tensile, psi 4930 Elongation, percent 2 Heat distortion, C74.5 Impact, ft. lb./in 0.383 Melt index 1.32

From these data, it is clear that the pyrolysis product tested (obtainedfrom polymer produced by process other than polymerization in thepresence of a chromium oxide catalyst) was interior, as a polystyreneadditive, to the pyrolysis product of this invention.

Example V Four runs were made to determine whether certain hydrocarbonpolymers were compatible with polystyrene. A description of each polymerand results obtained upon blending with polystyrene follow.

(1) A butadiene/vinylcyclohexene copolymer was prepared by thecopolymerization of 415 grams of butadiene with one liter ofvinylcyclohexene in the presence of 1 liter of n-heptane using 10 gramsof sodium dispersed in ml. of n-decane as the catalyst. A liquid polymerwas obtained. It was hydrogenated in methylcyclohexane solution in thepresence of a nickel-kieselguhr catalyst to give a product having anunsaturation of 6.2 percent. The material had a molecular weight of 878.It was blended on a hot mill (300 F.) with the general purposepolystyrene previously mentioned. Upon addition of a small quantity ofthe liquid polymer, the mixture became cloudy, indicating that thematerials were not compatible. Less than one weight percent of theliquid polymer was incorporated into the polystyrene.

(2) A sample of liquid polybutadiene prepared by sodium-catalyzedpolymerization was heated one hour at 10 mm. Hg and a temperature of 200to 380 F. During this period, there was a vigorous flow of nitrogenthough the polymer. The overhead condensate was hydrogenated inmethylcyclohexane solution in the presence of a nickelkieselguhrcatalyst. The hydrogenated product had an unsaturation of 15.5 percentand a molecular Weight of 232. It was blended on a hot mill (300 F.)with a general purpose polystyrene, as described above. A blend preparedusing 5 weight percent of the hydrogenated polymer, based on thepolystyrene, was cloudy, indicating incompatibility of the materials.

(3) A sample of liquid polybutadiene prepared by sopolymer caused themixture to form crumbs.

'7 dium-catalyzed polymerization was hydrogenated to give a producthaving an unsaturation of 8.7 percent. This product was blended withgeneral purpose polystyrene, as described in (1) above. Less than oneweight percent was added to the polystyrene. The materials wereincompatible, as evidenced by a cloudiness in the mixture.

(4) A sample of liquid polybutadiene prepared by sodium-catalyzedpolymerization was hydrogenated to give a product having an unsaturationof 26 percent. When an attempt was made to prepare a blend of thismaterial with polystyrene, one to two percent of the hydrogenated Thematerials were not compatible and a satisfactory blend could not beprepared.

The polymerization catalysts described in the foregoing examples inconnection with the preparation of polyethylene were prepared byimpregnating a precipitated composite of silica and alumina gels,comprising 90 weight percent silica and weight percent alumina, with anaqueous solution of chromium trioxide and subsequently heating atapproximately 950 F, for several hours in a current of substantiallyanhydrous air.

The foregoing examples demonstrate the utility of the pyrolysis productof this invention as a polystyrene plasticizer and illustrate thesuperiority of said pyrolysis product, as compared with pyrolysisproducts of polyethylenes produced by methods other than those describedherein, and as compared with certain other hydrocarbon mate- I'hemolecular weights of the polyethylenes used as starting materials forthe pyrolysis process disclosed in the foregoing examples werecalculated according to the following formula:

wherein M is the weight average molecular weight and N is the intrinsicviscosity as determined for a solution of 0.2 gram of the polymer in 50cc. of tetralin at 130 C. This type of molecular weight determination isdescribed by Kemp and Peters, Ind. Eng. Chem. 35, 1108 (1943), and byDienes and Klemm, J. Applied Phys. 17, 458 (June 1946).

From the foregoing, it will be seen that we have provided a novelpyrolysis product characterized by the substantial absence ofbranched-vinyl unsaturation; a process for preparing said product bypyrolyzing a polymer prepared by the polymerization of a l-olefin in thepresence of a catalyst containing chromium oxide as an essentialingredient; and a novel plasticized polystyrene resin compositioncontaining a minor, plasticizing amount of said pyrolysis product.Variation and modification within the scope of the disclosure and theclaims to the invention can readily be eifected by those skilled in theart.

We claim:

1. A composition comprising a polystyrene and a minor proportion,sufficient to plasticize said polystyrene, of a hydrocarbon which is athermal decomposition product of a polymer of a l-olefin, said thermaldecomposition having been at a temperature in the range of 700.to 900F., and said polymer having been produced by polymerization of saidl-olefin in the presence of a polymerization catalyst comprisingchromium oxide as an essential ingredient, said product having amolecular weight in the range of 200 to 800 and being characterized by amajor proportion of the unsaturation being selected from the groupconsisting of Trans-internal and V Terminal vinyl unsaturation.

2. A composition comprising a major proportion of a moldablehomopolymeric polystyrene and a minor proportion, suflicient toplasticize said polystyrene, of a hydrocarbon material, characterized bya major proportion of the unsaturation being selected from the groupconsisting of and C CH:

Terminal vinyl unsaturation, and by a molecular weight in the range 200to 800, said product having been prepared by the thermal decompositionat a temperature in the range 700 to 900 F., and a pressure notsubstantially greater than mm. Hg, of a polyethylene produced by thepolymerization of ethylene in the presence of a polymerization catalystcomprising chromium oxide as an essential ingredient thereof.

3. A composition according to claim 2 wherein said minor proportion isin the range 0.2 to 20 weight percent, based on said polystyrene.

4. A composition according to claim 2 wherein said minor proportion isin the range 0.5 to 8 weight percent, based on said polystyrene.

5. A method which comprises commingling at a temperature in the range to325 F., a major proportion of a polystyrene and a minor proportion,suflicient to plasticize said polystyrene, of a hydrocarbon product ofpyrolysis, at a temperature in the range 700 to 900 F., of a polymerproduced by polymerizing a l-olefin in the presence of a catalystcomprising chromium oxide as an essential ingredient, said producthaving a molecular weight in the range of 200 to 800 and beingcharacterized by a major proportion of the unsaturation being selectedfrom the group consisting of H: H o o Trans-internal and H: 0 CH,

Terminal vinyl unsaturation.

6. A method according to claim 5 wherein said olefin is ethylene, andsaid pyrolysis is conducted at a pressure and Terminal vinylunsaturation, and by a molecular weight in the range of about 200 toabout 800.

8. A solid plasticized polystyrene composition comprising a majorproportion of a solid polystyrene and a minor proportion, sufficient toplasticize said polystyrene, of a solid, waxy hydrocarbon product of thepyrolysis of a normally solid polymer of an olefin, said product havinga substantially linear carbon-chain structure and an average molecularweight in the range 200 to 800, the major proportion of the double bondsin said product being present in structures selected from the groupconsisting of H, H C /C Trans-internal and H2 /CH2 Terminal vinylunsaturation.

9. A normally solid plasticized polystyrene composition comprising amajor proportion of a solid polystyrene and a minor proportion,sufiicient to plasticize said polystyrene, of a solid, Waxy hydrocarbonproduct of the pyrolysis of a solid polyethylene, said product having asubstantially unbranched carbon-chain structure and an average molecularWeight in the range 200 to 800, substantially all of the double bonds insaid product being present in structures selected from the groupconsisting of H: H c o Trans-internal and Terminal vinyl unsaturation.

10. A plasticized polystyrene composition comprising a major proportionof a normally solid polystyrene and from 0.2 to 20 weight percent, basedon the weight of said polystyrene, of a solid, waxy hydrocarbon productof the pyrolysis of a solid polyethylene, said product having asubstantially unbranched carbon-chain structure and unsaturation.

11. A clear, transparent, plasticized polystyrene composition comprisinga major proportion of a normally solid polystyrene and from 0.5 to 8weight percent, based on the weight of said polystyrene of a solid,w-axy hydrocarbon product of the pyrolysis of a solid polyethylene, saidproduct having a substantially unbranched carbonchain structure and anaverage molecular weight in the range 200 to 800, substantially all ofthe double bonds in said product being present in structures selectedfrom the group consisting of 0 o H H2 Trans-internal and H2 0 CH:

Terminal vinyl unsaturation.

References Cited in the file of this patent UNITED STATES PATENTS2,353,228 Ducca July 11, 1944 2,372,001 Joyce Mar. 20, 1945 2,436,842Warner et a1. Mar. 2, 1948 2,691,647 Field et a1. Oct. 12, 19542,692,257 Zletz Oct. 19, 1954 2,752,315 Kuettel June 26, 1956 2,864,802Price et a1. Dec. 16, 1958 2,868,762 Oakes Jan. 13, 1959 FOREIGN PATENTS569,043 Great Britain Apr. 19, 1943 581,279 Great Britain Oct. 7, 1946127,820 Australia May 20, 1948 OTHER REFERENCES Rafi et al.:Polyethylene, High Polymers, volume XI, Interscience Pub. Inc., New York(1956), page 366.

UNITED STATES PATENTOFEICE i CERTIFICATE OF CORRECTION Patent No,2,994,679 st 1 ,1961

Rufus V. Jones et a1. It is hereby certified that error a ppears in theabove numbered patentvrequiring correction and that the saidLetters'Patent should read as "corrected below. v v

Column 8, lines 2 to 5, 20 to 24, d-56 6, 58, and column 9, lines 2 to 5and 25 to 28,f-m-,th'e formugl'a ;,ge'achy occurrence, should appea r asshown below ins tea d of as in the patent: 1

Signed and sealed this 6th day of March 1962. (SEAL) Attest:

ERNEST w. sWIDE DAVID L. LADD Attesting Officer Commissioner of Patents

1. A COMPOSITION COMPRISING A POLYSTYRENE AND A MINOR PROPORTION,SUFFICIENT TO PLASTICIZE SAID POLYSTYRENE, OF A HYDROCARBON WHICH IS ATHERMAL DECOMPOSITION PRODUCT OF A POLYMER OF A 1-OLEFIN, SAID THERMALDECOMPOSITION HAVING BEEN AT A TEMPERATURE IN THE RANGE OF 700 TO900*F., AND SAID POLYMER HAVING BEEN PRODUCED BY POLYMERIZATION OF SAID1-OLEFIN IN THE PRESENCE OF A POLYMERIZATION CATALYST COMPRISINGCHROMIUM OXIDE AS AN ESSENTIAL INGREDIENT, SAID PRODUCT HAVING AMOLECULAR WEIGHT IN THE RANGE OF 200 TO 800 AND BEING CHARACTERIZED BY AMAJOR PROPORTION OF THE UNSATURATION BEING SELECTED FROM THE GROUPCONSISTING OF